1. Field of the Invention
This invention relates to a fluid pressure sensing and of establishing an electrical measure thereof.
2. Description of the Prior Art
Fluid pressure sensing refers to both gas and liquid pressure sensing.
Fluid pressure sensors in the prior art have typically relied on the amount of displacement of one part with respect to another caused by a sampling of the applied fluid. For example, fluid under pressure is applied to a chamber having a diaphragm as one of its walls, the external side of the wall being at ambient pressure condition. The diaphragm typically has attached to it a wiper connection of a potentiometer. Movement of the diaphragm, and hence the wiper carried thereby, changes the electrical resistance characteristics of a network including the potentiometer. This change can be reflected in a voltage change, which, in turn, drives a meter. Alternatively, the analog voltage can be converted to digital format for processing in a digital controller or the like.
Alternative to the diaphragm carrying a movable element of a resistor, diaphragms employed in the prior art have carried one plate of a capacitor. Movement of the diaphragm moves this plate closer to or further from a stationary capacitor plate, resulting in the change of capacitance. This capacitance change can be metered or used in a manner similar to the resistance change discussed above.
Also, magnetic response of an electromagnet caused by movement of a movable core carried by a diaphragm operating in a coil has also been used in prior art pressure sensors.
The movement of the diaphragm is not linear with pressure change, since as the outward distance from an at-rest starting point grows, the stiffer the diaphragm becomes. Moreover, the entire diaphragm does not normally move outwardly uniformly since it is stationarily connected at its periphery, further defeating linearity of response. Such non-linearity is either disregarded or compensated for in prior art sensors using movable resistance, capacitance or magnetic elements.
It is also evident that each of the components discussed above carried by prior art pressure sensing dipahragms are somewhat bulky, thereby slowing down the response to pressure changes due to inertia and even affecting the response sensitivity of the sensor.
One type of electrical circuit that is often used in conjunction with one of the mechanical sensing arrangements described above includes a tuned circuit. The movable elements connected to the diaphragm varies the frequency of the output. In order to use this frequency change in a meter of common utilization systems, it is necessary to have a frequency-to-voltage converter and, in some cases, an additional analog-to-digital voltage converter operation in conjunction with a computer.
Therefore, it is a feature of the present invention to provide an improved fluid pressure sensor in which the measurement of pressure is independent of the amount of or linearity of diaphragm movement.
It is another feature of the present invention to provide an improved fluid pressure sensor which develops a digital-type output signal for metering or use purposes without going through a conversion either from a frequency change or an analog voltage change.
It is still another feature of the present invention to provide an improved fluid pressure sensor which uses a stiff diaphragm of minimum bulk carrying only an electrical contact and no other electrical or magnetic parts, thereby providing ruggedness and fast response, and eliminating requirements for diaphragm, electrical and magnetic linearity.